The present invention relates to a toner residual quantity detection method in an image forming apparatus such as a printer or a digital copying machine.
When copying an original document by using an image forming apparatus, an original image is first read by a scanner portion, and corresponding image data is provided. In a printer portion, an electrostatic latent image is formed on a photosensitive drum by using light beams emitted in accordance with the image data. A toner is caused to adhere to this electrostatic latent image by a developer, and a toner image is formed. The toner image is transferred onto a paper sheet by a transfer portion, and fixed on the paper by a fixing portion. In this manner, a copy image is printed on the paper.
During printing an image as described above, a toner residual quantity is detected in the developer. When it is determined that the toner residual quantity is insufficient, the toner is supplied from a supply toner cartridge.
If toner detection is carried out during printing, a toner sensor may erroneously operate due to affects of noise from, e.g., a development high-voltage power supply and a paper carriage motor drive system. When the toner sensor malfunctions, it may be determined that the toner residual quantity is insufficient even though the toner residual quantity is sufficient, and an unnecessary supply operation may be executed in some cases.
For example, if there is a poor contact at a contact point of a high-voltage supply path used in a development process, an induction noise may occur due to electric discharge, and the toner sensor which operates with a small voltage and a small current may malfunction.
Further, in order to reduce an influence of such noise, a special component is needed for the toner residual quantity detection circuit, and special attention must be paid to the sensor arrangement and wiring.